The pope said 500 years ago, on January 22, 1506, Pope Julius II welcomed and blessed the first contingent of Swiss guards, who arrived in Rome to protect him and the apostolic palace.

Earlier, a special mass was held in the frescoed Sistine Chapel for them and their families to commemorate the founding anniversary.

During the mass, the Swiss Guard's chaplain said that for the past 500 years, with loyalty and authentic religious spirit, young Swiss men have crossed the Alps, to offer with enthusiasm, their humble service to the Vicar of Christ.

The Swiss Guards have protected 42 popes. Today, 110 guards make up the Vatican army, which is called the smallest and oldest in the world.

Pope Benedict also told the faithful that this Sunday came in the middle of the week of prayer for Christian unity, when Christians of different denominations all over the world pray and reflect together.

We must not doubt, the pope said, that one day we will be one.

The Pope then told the faithful that his first encyclical titled "God is Love" will be published Wednesday on the feast of the conversion of Saint Paul. That day, the Pope will celebrate vespers in the Basilica of Saint Paul with representatives of other Christian churches.

Addressing the pilgrims gathered in Saint Peter's Square, Pope Benedict also said that among the many international concerns, his thoughts had again returned to Africa.

He said he was thinking in particular of Ivory Coast, where serious tensions persist among the country's various social and political groups. He urged all those involved to pursue a constructive dialogue to reach reconciliation and peace.